I had something similar on Saturday when I genuinely forgot to use the app to pay for my parking in Preston Park. No real excuses from me, I was going to chalk it up to bad luck and pay the fine now while its cheaper
Appeal. My Mrs typo'd her registration in the app and got a ticket. Called up and appealed, they could see she'd paid but used the wrong registration so let her off with a warning to be more careful in the future as next time they won't let her off.
I would definitely appeal and provide their details so they can independently check that that registration number had paid at that time. The obvious downside is that there's no proof that the registration number entered wasn't also parked there - but they might show some mercy.
Nothing lost through appealing though, the discounted rate is frozen whilst the appeal is ongoing. Always appeal - you have nothing to lose.
I had something similar on Saturday when I genuinely forgot to use the app to pay for my parking in Preston Park. No real excuses from me, I was going to chalk it up to bad luck and pay the fine now while its cheaper